1. Field of the Invention
The present invention relates to a clock detection device of an information recording/reproducing apparatus and a clock detection device of an information recording apparatus adapted to an apparatus for recording/reproducing information to and from a recording medium or an apparatus for recording information and capable of detecting a reproduction clock and a recording clock.
2. Related Art Statement
An optical recording/reproducing apparatus, such as an optical disc, a photomagnetic disc or an optical card, comprises a light source that illuminates an optical recording/reproducing medium (hereinafter called a medium). Further, its non-storage-type detector, such as a silicon photodiode, is used to convert photoelectrically information on the recording medium surface. Then, information is processed so that data is read out. Maintenance of focusing of a reading beam and following to the track are performed in such a manner that an error signal is formed from a detection signal of the foregoing detector and the error signal thus-formed is fed back to an optical head. FIG. 1 illustrates an example of a medium format having an arrangement that data pits 51 and clock pits 52 are recorded together, the medium format being formed by two vertical sections each having 8 data lines with respect to a clock line 53. Sixteen vertical data items are determined by one clock edge. Reference numeral 54 represents a light spot of the reading beam.
FIG. 2 illustrates a state where the surface of the recording medium is projected so that the detection detector is explained. The difference in the reflectance of the data pits 51 is used to indicate "0" or "1" of data, the data being detected by 16 data cells 55 disposed lengthwise. Four cell groups 56 for clocks, each of which is consisting of two cells, are disposed to detect the clocks. The edge of the clock signal reproduced by the cell group 56 serves as the data deterministic timing.
FIG. 3 illustrates the structures of an optical head 60, a detector, a reproducing system and a servo system.
In the optical head 60 shown in FIG. 3, light beams emitted from a light source 61, for example, a light emitting diode (LED), are made to be parallel beams by a collimator lens 62. The light beams, emitted from the light source 61 and allowed to pass through the collimator lens 62, pass through a beam splitter 63, the light beams being then allowed to pass through an objective lens 64 to be applied to a recording medium 65. Light reflected from the recording medium 65 passes through the object lens 64, reflected light bening then reflected by the beam splitter 63, allowed to pass through an imaging lens 66, and introduced into a detector 67. The imaging lens 66 projects an image on the medium surface onto the detector 67.
The detector 67 comprises 16 data cells shown in FIG. 2, the four clock cell groups 56 and servo cells C1 to C4 and D1 to D4. A tracking actuator 68 controls the movement of the object lens 64 in the directions perpendicular to the track to cause the light spot 54 on the surface of the detector 67 to follow the track while preventing a perpendicular deviation from the track. A focusing actuator 69 acts to move the object lens 64 in a vertical direction with respect to the surface of the recording medium 65 to align the focal point of the light spot 54.
The cells C1 to C4 are positioned outside the edge of the optical spot 54 as shown in FIG. 2, while cells D1 to D4 are positioned inside the light spot 54.
The servo system of the apparatus shown in FIG. 3 comprises an I/V conversion circuit 70 for servo cells that converts the output currents from the cells C1 to C4 and D1 to D4 into voltages, a tracking error (TE) signal generating circuit 71, a drive circuit 72 for the track (Tr), a focus error signal generating circuit 73 for receiving a voltage signal supplied from the I/V conversion circuit 70 for the servo cell, and a drive circuit 74 for focusing (FO). The reproduction system of the apparatus comprises an I/V conversion circuit 75 for reading that converts the output currents (reading signals) from the reading cell group 55, a binary coding circuit 76 for binary-coding the reading signals, and a reading circuit 77 for reading data in response to the binary-coded reading signal and a clock signal (omitted from illustration).
The operation of the foregoing apparatus will now be described.
Since the change of the focus position changes the diameter of the beam on the detector surface, the focusing servo detects the foregoing change. Therefore, feeding back, so performed that the difference of the cell disposed at the edge of the beam and shown in FIG. 2 is made to be zero, enables the focusing position to be maintained. Specifically, the focusing servo obtains the difference (.SIGMA.C -.SIGMA.D) between sum signal .SIGMA.C of the cells C1 and C4 and sum signal .SIGMA.D of the cells D1 to D4, the difference being obtained as an error signal to be fed back to the drive actuator for focusing.
The tracking servo is so performed that the clock pit 52 equally corresponds to the cells D1 and D2 and similarly to the cells D3 and D4. Therefore, the track servo feeds back {(D1+D3)-(D2+D4)}, as the error signal, to the drive actuator 68 for tracking.
When data is read, the read-clock is first generated, the read-clock being obtained by binary coding the difference between the sum of even-numbered clock cells 56 and that of the odd-numbered clock cells 56. The 16 data items are respectively binary-coded, and sampled at the edges of the first and last transitions of the clock so that discriminated data items are obtained. Since correction bits are added to the data and both interleaving and modulation are performed, demodulation, deinterleaving and error correction cause reading to be completed.
The following capability can be considered with an information recording/reproducing apparatus of the foregoing type in which the data reading timing of which is determined in accordance with the clock reproduced from the clock line on the medium. That is, if the structure is intended to be capable of both reproducing and recording data, the clock lines on the medium are utilized to serve as the write-clock for determining the recording timing.
With reference to FIG. 4, description will be made about data recording and reproducing operations to be performed when the read-clock from the clock line on the medium surface is used as the write-clock.
In FIG. 4, (a) shows a write-clock for determining the recording timing, the write-clock being generated in accordance with a reading signal obtained from the clock line on the medium. Pits written in synchronization with the write-clock are shown in (b) of FIG. 4. A reproduction signal shown in (c) of FIG. 4 is obtained by reproducing the pits shown in (b) of FIG. 4, the reproducing signal being binary-coded and sampled at the first and last transition edges to be made discriminated data. A reading clock (d) is a clock generated from the same clock line from which the write-clock (a) has been generated. Therefore, the first and last transition positions of the read-clock (d) coincide with the ends of the pits shown in (b) of FIG. 4.
However, the state shown in FIG. 4 is weakest against the phase change of the read-clock (d), and therefore, a slight phase change causes an error to occur in the definition of the reproducing signal. Thick characters in the results of reading (e) indicate errors.
The data detection method shown in FIG. 4 is a method so arranged that edges of the data reproducing clock obtained by reproducing the clock pits recorded on the recording medium are used to detect whether or not data is present on the recording medium. There is another type of information recording/reproducing apparatus adapted to a method that uses a window generated in accordance with clock pits to detect whether or not data is present on the recording medium.